self-protection paste boronizing technology. Therefore, the research and development of new low-temperature self-protection paste boronizing technology is of important engineering application value. 2 Experimental details Thermal power plant boiler economizer tube blasting operation pipe (20 steel annealing states) was used as boron material. B C4 、 4 KBF 、 the activated carbon,、SiC、 2 3 Al O (filler), sodium silicate solution (adhesive) and a certain amount of lanthanum rare earth were prepared for boron paste, then the prepared cream boron paste was evenly coated on the surface of the sample, thickness is 3 ~ 5 mm, as is shown in Fig.1. The coated boron sample was dried in the drying oven at 160℃, and then moved into carbon silicon rod furnace to be heated for boronizing. The boronizing experiments were made in a series of set temperature. After a certain period of boron heat preservation time, electric power supply were turned off. When the samples in the furnace were cooled to 100 ~ 200 ℃, they were removed to cool in the air. Then the protective layer and paste layer were removed to prepare metallographic specimen which was to be corroded with nitric acid of 5% alcohol. Then the 200 MAT inverted metallographic microscopes was used to observe the microstructure of the boron samples, and the HBRV 187.5 hardness tester was used to test the hardness of the boron samples. Fig.1 Schematic diagram of the specimen surface coating 3 Results and discussion 3.1 Temperature’s influence on the boron effect without the rare earth With no rare earth added, the microstructures of the self-protective paste boron sample are shown in Fig.2. 保护层 膏剂层 试件 Protective layer Paste layer Specimen 10µm (a) 10µm (b)
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